1. Field of the Invention
The present invention relates to fully implantable hearing aid system, and more particularly to an electret microphone adapted for use in such fully implantable hearing aid systems, and how such an electret microphone or other type of microphone may be incorporated into the fully implantable hearing aid system.
2. Description of the Prior Art
Patent Cooperation Treaty (xe2x80x9cPCTxe2x80x9d) patent application Ser. No. PCT/US96/15087 filed Sep. 19, 1996, entitled xe2x80x9cImplantable Hearing Aidxe2x80x9d (xe2x80x9cthe PCT Patent Applicationxe2x80x9d) describes a fully implantable hearing aid system which uses a very small implantable microactuator. The PCT Patent Application also discloses a Kynar(copyright) microphone which may be physically separated far enough from the implanted microactuator so that no feedback occurs. The fully implantable hearing aid system disclosed in the PCT Patent Application can operate for a period of five years on a set of batteries, and produce sound levels of 110 dB. The fully implantable hearing aid system described in the PCT Patent Applications is extremely compact, sturdy, rugged, and provides significant progress towards addressing problems with presently available hearing aids.
While the Kynar microphone disclosed in the PCT Patent Application enables an operable fully implantable hearing aid system, that system""s performance may be improved through the use of a more sensitive electret microphone. U.S. Pat. Nos. 4,947,478 (xe2x80x9cthe ""478 patentxe2x80x9d) and 5,015,225, a division of the ""478 patent, disclose incorporating a conventional electret microphone into an outer ear canal unit 34 of a partially implantable hearing aid system. U.S. Pat. No. 5,408,534 entitled xe2x80x9cElectret Microphone Assembly, and Method of Manufacturexe2x80x9d discloses an improved structure and method for coupling a charge plate of the electret microphone used in a hearing aid to an input terminal of an impedance matching circuit or internal amplifier. One difficulty with using an electret microphone for a fully implantable hearing aid system not addressed by the patents identified above is that the microphone must be hermetically sealed to prevent electret de-polarization while simultaneously permitting sound waves to impinge upon the microphone.
Because the hearing aid system disclosed in the PCT Patent Application is fully implanted, it is presently estimated that after a five year interval of use the system""s battery may likely need replacement which necessarily involves surgery. Another aspect of a fully implantable hearing aid system is ensuring reliable electrical interconnection of the system""s microphone and microactuator to the system""s signal-processing amplifier throughout a five year interval prior to battery replacement, and subsequently after the battery has been replaced.
An object of the present invention is to provide an electret microphone adapted for incorporation into a fully implantable hearing aid system.
Another object of the present invention is to provide a simpler fully implantable hearing aid system.
Another object of the present invention is to provide a fully implantable hearing aid system which incorporates the microphone into an implanted housing that contains the hearing aid""s amplifier and battery.
Another object of the present invention is to provide an improved structure for implanting a housing enclosing a fully implantable hearing aid""s amplifier and battery into a depression surgically sculpted in a subject""s mastoid cortical bone.
Another object of the present invention is to provide a structure for a fully implantable hearing aid""s housing that encloses an amplifier and battery which provides ready tactile access to hearing aid operating controls.
Briefly, the present invention includes a sealed microphone adapted for inclusion in an implantable hearing aid system. The sealed implantable microphone provides an input signal to an amplifier included in the implantable hearing aid system. The microphone includes a diaphragm having a thin central region surrounded by a thicker rim. An electret, which is bonded to the diaphragm, contacts a roughened plate included in the microphone. The rim of the diaphragm is bonded to a surface of a housing to hermetically enclose the electret and the plate, the plate being electrically insulated from the housing. The microphone also includes an electrical connector coupled both to the plate and through the housing to the electret for providing the input signal to the amplifier of the implantable hearing aid system.
This implantable microphone is preferably incorporated into a hermetically sealed electronics module. In addition to the microphone, the electronics module includes an amplifier that receives the input signal from the microphone""s plate and the electret, and provides an output signal to a microactuator also included in the implantable hearing aid system. The electronics module also includes a battery for energizing operation of the implantable hearing aid system. A housing for the electronics module receives the battery, the amplifier, the plate, and the electret. The microphone""s diaphragm forms a surface of the housing with the rim of the diaphragm being bonded to the housing thereby hermetically sealing the electronics module. An electrical connector coupled to the amplifier provides the output signal to the microactuator of the implantable hearing aid system.
These and other features, objects and advantages will be understood or apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.